The invention relates in general to gas indicators and in particular to a new and useful indicator for the documentation of chlorine by discoloration of potassium iodide applied on a support.
Such an indicator is described in German pat. No. 1 001 507.
The known indicator serves to detect chlorine in air. To this end, a support material, for example silica gel, is impregnated with a potassium iodide solution and filled into a test tube. When chlorine containing air flows through the test tube, free iodine is separated and colors the silica gel layer light brown. As this discoloration is not stable enough to obtain a clear indication for the determination of the chlorine content, the support is impregnated additionally with a starch solution. Now, due to the action of the released iodine on the starch, an intensive and distinct stable blue coloration of the impregnated support occurs.
With the known indicator, the fact that for stable addition of the starch on the support a further addition of zinc chloride or of mercury iodide becomes necessary is disadvantageous. This stabilization addition, however, cannot prevent the situation that, when very high chlorine concentrations are over the known impregnated support, the coloration bleaches out, thus preventing a permanent indication.